CROSSOVER FROM RANDOM FIELD TO SPIN-GLASS BEHAVIOR IN FEXZN1-XF2

It is well known that the diluted antiferromagnet FexZn 1-xF2 under an external field is a prototype random field Ising model system (RFIM) when the concentration x is larger than ≅0.4. Here we show that as x decreases there is a crossover to spin-glass (SG) behavior. For x=0.25 the dc magnetization has irreversibility, metastability, and remanence typical of a canonical SG whereas for x=0.48 they are characteristic of a RFIM system. The ac susceptibility also shows completely diverse behavior for x=0.25 and 0.48, characteristic of SG and RFIM system, respectively. The SG nature of the x=0.25 sample is confirmed by the critical behavior of the nonlinear dc susceptibility above the SG freezing temperature T≅10 K. Finally, for x=0.31 there is a temperature dependent crossover from RFIM to SG behavior.